Oxidation of phthalide and mixtures thereof to phthalic anhydride



This invention relatestb the production oi'plithalieacid and phthalic anhydride,

It is an object of s mia -same rov de-anew proc es's for the production ofiphthalic acid -1" phthali'c anhydrride-v .n. t a

Anotherobject'of thisinvert tionis'tlie provision oiia new eflicient and economical processtfor theproduction offphthalic" acid" o phthalic anhydride by the oxidation ofo-xylene with anoxyg'en-containing gas p. l

.Other objects'of this invention will be apparent fro'nt the following detailed description and claims, In this description and clair'ris all proportions are by weightu'riy less otherwise indicated. j I

In accordance with one'aspect of this invention-phthalic anhydride is produced by the oxidation of phthalide, preferably by reaction of oxygen witha liquid comprising" phthalide; In onepreferred embodiment, this reaction is carried" out by bubbIingan" oxygen-containingigas through a mixture of o-x'ylene, o -toluic acid and phthalide, at an elevated temperature. and under superatmosplieric pressure, in the presence ofasuitable oxidation catalyst.

Itis found that the re'actiom'proceeds smoothly and rap.-

the mixture-is very' high (61g- -c'onsiderably above;3:1,

for example about 4*to'6zl o'i' higher). It is also found that the' phthalic anhydrideremains dissolved in the; reaction mixture;

"In accordance with' anotheriaspect of this invention, after an o-xylenewon'taining? material issubjected to partial oxidation to form" a mixture containing phthalic anhydridein solution, the phthalic'anhydride is separated from said'mixture by subjecting itto hydrolysis to pro duce phthalic acid, which is removed, preferably in aqueousphas; Theremaining': portion of the mixture is 'then*blended"with a'=further'quantity:.of o.-xylene and: subjected to" further oxidation.-

ingi'gas'is -passed"through a mixture containing o-xy-lene, o toluic acids and phthalide'; 1 as described previously, in a reaction zone; ,astream of" the 'productsis withdrawn continuously front: the reaction-zone and subjected to hydrolysis and watereextraction-to form anaqueous'phase containing phthalicf acid-and a:- nonaqueous' phase containingt" o-xyler'ie; o-tdluic, acidrand' phthalide. After separation of the 'aqueousplia'se; :the phthalic acid a rec6ve'rec:l*'therefrom in'suitable'manhen as by evaporation of: the? water and'r'ecdr'iversion of-thephthalic acid to phthalic-an'hydride. l i

- The-1 proportions of the components of the mixture undergoing foxidation may bevarid widely. Preferably, atleast about -%;of ;-phthalide;is present: inrthis mixture,

Advantageously; the; processis 'carried" on continuously. Thus, inone pre ferre'd embodiment of the invention, 1 an oxygent-containmixture. I p 1 oxidizable under, the conditions or reaction, may be,

presentiif ide'sired, excellentresult's have been obtained] 7 the'present invention;

2,925,425 Patented Feb. 16,,1-9eo or between plithalid and 1 phthalic: anhydiide orautoesters of pht'halide-i These esters are convertible tov phthalic' anhydr ide when they are present in the reaction; mixture of}v this invention. Breferably the o-xylene; ortoluic acid and phthalide', taken together-,fl constitute'.atZ least about 80%. ofiithe, oxidizable compounds of the Although an inert solvent, substantially non-t without" the use of solvent, and the elimination of necessity for usingQs'olventi's' an important advantage of k As stated, it is preferable-to use an oxi dation catalyst; Such, catalysts, may be of ,the well knov'vnltype' general employed for oxidation} ofjhydrdcarlbons or other org an .mmp d is i h an. X s 0 i gas? O h se cla'talyst'sl-the'rnosjt important group. contains, a metal, which existsin atil ea'stl we valence states,,such as cobalt, man ganese, nan, chromium nickel or, copper. Although such] metal's ,,have.cataly c; properties when used alone? they, are. generally employedi'jn'compound form, elg, as} salts, Qobalt salts, such: as cobalt acetate and cobalt naphthenate have been fc u1;1d.to.f,be particularly useful for thepra cticeof invention, These materialsgneed onlyfbeapresentinlsmall amouhts, for example, 0.001 to 110%, based on the wei'ght'of the reaction mixture; a

The oxygen containinggas. is desirably air, for reasons of economy,, butfother gases-,qsuch as pure. oxygen or-air enriched. with oxygen may be usd. ,"The oxygen-contain? in gas an be distributed through the, liquid mixture; beingoxidize'd in; suitable manner, as by introducing,

' the gasthroughaspargeror ame plate into the bottcnr oframass of theliq I V in a'r'iy i applrf o'p'riate reactionvessel, which may, tcoii tainjBerl saddles or otherpacking material to incre 'asewth e extent oicontact between the gas. and,

a 'essure and temperature off 'th'e oxidation rlaqtion m y be variedjwidely. :I t, is, preferable to use super:

a utlfi 0,1 15," 1 H QWater s forrfnedby ftlieoxidation reaction. It-is ratmd that when'th e proportionofiwater in the reaction mixture builds up, for example to Ste 10%, the rate of reaction: isIreduced-cqnsiderablyr Accordingly, it is desirable removewat'efofthereaction as it 'isforrned; this maybe done, conveniently by continuously distilling. ofi a turei'of xylene" and? water duringvthe reaction, allowing the, distillate to'separate into'tv'v'o phases,returning,the organic non-aqueousg phase, to the. reactionmixture and discarding or otherwise treatin'gthe'water phase, which;

ma contain dissolved acetic and formic acids as'well as other degradationproducts.

stated," the, oxidation reaction may be carried out continuously,,as by feedi'n'g a mixture of the o-xylene; o-toluic acid and phthalide continuously to the. reaction; zone continuously withdrawing from said zone. a phthalicfanhydride coi1taining mixture which has a lower o x'yl contentthan the feed mixture. For best results the'jc riipbsit not the feed mixture should be so conratie o f supply o fo-tqluic acid. andphthalideintlieffeed,

'mixtureissubstantiall'y, equal'to the rate at which th; e;

andit -isa-lso desirable'that 'this rnixture contains at least I about 5% each-mi o-toluicracid" and-o-xylene; There mamb be m a t-i it es u a lmsh and oxidation products thereof, as w'ell as; various 0th r p'artial reaction-products such asvestei s formed by,

proportions are" us a -ediiversm af a xylhetd plithalii-auhydridz ,Forarty' trollediin relation to theconditions of reaction thatithiel,

constituents afreiwithdrawn, c'ontaining iX I rom t ,4

' 9 t e is v e ium nd assa e .thr'ough the oxidation 10 i l i ha e a given set of reaction conditions these proportions can be determined by successive experiments involving removal of the phthalic anhydride from the withdrawn re action mixture and recirculation of the remainder of the withdrawn mixture, blended with any selected proportion of o-xylene, until the aforesaid equilibrium is reached. Generally, it is found that at equilibrium conditions the ratio of o-toluic acid to o-xylene in the reaction mixture is relatively high, for example about 4:1 to 8:1. Thus, under the generally preferred reaction conditions the relative amounts of the constituents of the equilibrium reaction mixture are about 8 to 13 parts o-xylene, 57 to 61 parts o-toluic acid, 21 to 28 parts phthalide and to 7 parts by Weight of esters formed in the reaction, probably iiiairily esters of phthalide with itself or with phthalic or o-toluic acids and having a molecular weight above 240 and boiling above 290 C. These proportions were obtained in a system operating at a reaction temperature of 160 C., a pressure of 50 p.s.i.g. and a 27.5% conversion (per pass) of the o-xylene to oxidation products, using air as the oxygen-containing gas and 0.025% cobalt naphthenate as the catalyst, and removing all the phthalic anhydride from the withdrawn mixture before fecirculating. Of course all the phthalic 'anhydride formed need not be removed, and a minor proportion thereof may be recirculated with the other components of the reaction mixture if desired. Phthalic anhydride is stable under the conditions of the oxidation reaction and the recycling thereof has not substantial effect on the efiiciency of the reaction, however, the dilution of the feed mixture by the phthalic anhydride, due to recycling will decrease the effective concentration of the other components and therefore decrease the rate of formation of this compound to some extent, and it is preferred to maintain the concentration of this component in the reaction mixture at below about 15% Hydrolysis takes place on heating with water. In order to accelerate the hydrolysis, temperatures above about 80 C. are preferred; when temperatures above 100 C. (e.g. 150 C.) are desired, the hydrolysis should be conducted at supermospheric pressure to maintain the mixture liquid. The conditions of hydrolysis should be such as to cause no substantial hydroysis of the phthalide or of the other esters mentioned above, since this would convert these materials to compounds more soluble in water and therefore more extractable by the water used in the extraction step.

The hydrolysis of the phthalic anhydride and the extraction of the resulting phthalic acid from the rest of the reaction products may be effected as a single-step operation. It is generally more efficient to pass the mixed reaction products first to a hydrolysis zone and then tov a zone where an aqueous phase containing the ophthalic acid is separated. Thus, in one procedure a small amount of water is added to the mixed reaction products and the resulting mixture is maintained at an elevated temperature to effect at least partial hydrolysis of the phthalic anhydride, following which the mixture is fed from hte hydrolysis zone to an extraction zone; e.g. a zone Where the reaction products are extracted counter-current with water or other suitable liquid; of course, in this case, some hydrolysis may occur in the extraction zone. Alternatively hydrolysis may be efiected in the presence of a large amount of water in the hydrolysis zone, and the resulting mixture may be fed to a separation zone, where it is allowed to separate into two phases: an aqueous phase containing the o-phthalic acid, and a Water-immiscible phase containing the other constituents.

Separation of the aqueous phase from the water-immiscible may be carried out over a wide range of tern peratures. If desired elevated temperatures may be used and it is found that the best separations, from the: point of view of solubility of the o-phthalic acid in e ttle a sde e a t hes lub itrs u e he Oth r 1 so that the aqueous phase contains a relatively high conin the extraction with o-xylene.

centration of o-phthalic acid (e.g. about 10 to 20%), but without actually causing crystallization of o-phthalic acid from said aqueous phase during the extractions. To this end a temperature of about to 120 C. is desirable When a water-soluble catalyst, such as cobalt acetate, is employed for the oxidation reaction some of this catalyst will appear in the aqueous extract.

The m-xylene (or p-xylene) and its partial oxidation products, which may be present asimpurities in the reaction mixture, tend to form isophtalic acid,-which is in soluble in the other reaction products and which may therefore be removed by any suitable methods, e.g. filtration, preferably before the hydrolysis step. It is preferred that the m-xylene and p-xyl'ene' content in the feed be low, e.g. below about 10% based on the 'o-xylene. Preferably, the fresh feed to the oxidation zone contains at least about o-xylene. o-xylene, containing minor amounts of m-yxlene, ethyl benzene and eightcarbon aliphatic hydrocarbons, isvery suitable.

As stated, the phthalic acid may be recovered from the aqueous phase by evaporation of the water and 'reconversion of the acid to-its anhydride. This may be done under normal or superatmosphericpressure. The water also may be removed by azeotropic distillation, or the phthalic acid may be removed from solution by crystallization.

The following examples are given to illustrate this invention further.

7 Example I A liquid mixture containing 10.0% o-xylene, 60.0% o-toluic acid and 30% pthalide, to which is added 0.05 based on the weight of the mixture, of hydrated cobaltous acetate, Co(C I-I O -4H O, is oxidized at a temperature of 160 C. under a pressureof 50 p.s.i.g. by bubbling air through a column of said liquid mixture contained in tubular reactor, 2 inches in diameter and constructed of stainless steel (type 316). The air is admitted through a sparger mounted 28 inches below the level of the liquid in the column. The column is fitted with a condenser through which the gaseous efiluent from the column is passed, and in which the water of reaction, xylene and any other organic materials are condensed; the condensate forms two phases, the water phase being discardedand the xylene phase being returned continuously to the reaction mixture. The liquid mixture is fed continuously to the top of the column and reaction products are withdrawn continuously from the bottom. The air is passed through the column at the rate of 18 cu. ft. per hr. The residence time of the liquid in the column is 37 minutes. 18% of the oxygen supplied is reacted. The rate of oxygen consumption in cu. ft. per. minute per sq. in. of cross-sectional area ofthe reactor is 3.4 l0- 1 27.4% of the o-xylene present in thefeed mixture is reacted, the composition of the reaction product being 7.2% o-xylene, 60.7% o-toluic acid, 30.0% phthalide, 1.0% phthalic anhydride and-1.1% of a mixture of esters boiling above 290 C., so that for each moles of o-xylene consumed there are obtained 27.5 moles of o-toluic acid, 3.6 moles of phthalide, 27.3 moles of phthalic anhydride and 16.0 moles of said esters (calculated as molecular weight 270). The carbon recovery is 95.4%; i.e., calculated on the basis of the carbon in the o-xylene which has been oxidized, the carbon in the waste products (C0, C0 acetic and formic acids) represents only 4.6% 5 i calculated on the basis of the carbon in the mowers totalreaction mixture;.the-carbom lost in the wast products represents 0. 16'% orthe tota1 carbon iir tlre mixture; I

. Example II}v I v i Example I; is repeated, -except?thatigthesfeed mixture contains 9.8% ortho-xylene;,57.2%fo toluic;acid;.25.7%

phthalide, 0.7% phthalic anhydride: and; 627% :ofithe l 25.4% of then-xylenepresentin theifeed mixtureris 1 reacted; and for each 100 .moles? of o-xylene consumed there are obtained 2.1 moles of o-toluiciacid; 15.3. moles phthalideand -:-73.5 mo1es of phthalic anhydride, .at a carbon recovery of 90.9%. v L

Example III v Example-II is repeated except that the feegl contains 8.8 o-xylene, 54.0% o-toluic acid,';27;5% phthalide, 4.1% phthalic anhydride;and 5.6,%g' of -the esters, to which is added 0.05%..cobaltous naphthenate 38;0% of the o-xylene in thefeed mixture;is"reacted,

and for each 100 moles of o-xylene; consumed there are obtained 32.4 moles o-toluic-acid, 37.5 moles phthalic anhydride and 12.5 moles-of the esters, and n additionaI,

phthalide, at a carbon recoveryof 95.9% t j Example I V Example I is repeated except'that thefeed mixture. con; tains 40% phthalide and 60% meta-xylene to WlillChtlS added 0.0 5 of cobaltous naphthenate, and -38%.-'of the oxygen 'supplie dis reacted.

7.4% of the phthalide present in the. feed mixtureds reacted, and phthalic anhydride is formedat'an efficiency. of 92% basedon the proportion of phthalide reacted, assuming that none of the v meta-xylene: is converted to' phthalic anhydride; H Example; V.

A mixture of 48% 0 -Xylene, 26% phthalideand 26% o-toluic acid, to which 0.025 %-"cobaltous naphthenate has been added, is oxidized under-the conditions described in Example I. The yield of "phthalic anhydride, based on the amount ofo-xylene reacted, is 18. 7%.

' Example VI A reactor product obtainedby oxidation similar to that in Example III is -mixed with' hot" water to produce a mixture containing 69% o xylene, 50.2% o-toluic {ale-id,

27.6% phthalide, 4.8% of the esters, 8.8% phthali'cian hydride and 1.7% water. The resulting mixture is maintained at a temperature of 100 C. for 15 minutes, and then passed continuously through a York-Scheibel liquidliquid extractor, at a temperature of 90 C., counter-current to a stream of distilled water, the latter being supplied to the extractor at a feed rate which is 92% the feed rate of said reactor product. From the bottom of the extractor there is obtained a stream of organic .phase containing 7.1% xylene, 46.4% o-toluic acid, 25.0% phthalide, 9.4% ester, 3.2% phthalic anhydride and 8.9% water. This organic phase is dehydrated by azeotropic distillation with o-xylene (containing small amountsof o-toluic acid and phthalide and obtained from the second extractor described below) and is. then recycled to the reactor for further oxidation.

From the top of the extractor there [is obtained an aqueous phase containing 6% phthalic acid, 3.4% otoluic acid, 2.2% phthalide and the balance water. This aqueous phase is fed continuously to the top of a second York-Scheibel extractor, operated at a temperature of 90 C., where it is extracted, countercurrent, with an equal weight of o-xylene. .From the bottom of this second extractor there is obtained a stream containing 6.4%

o'-toluic}'acid aswellas the phthalidei ExainpI VIIQ A recycle mixture, obtained as described belovL-and containing .o x-ylene, o-toluic'l acid; phthalide,- phthalic anhydridefand r'the esters describedin? Example -I, together withcobalt naphthenateas: catalyst;isrfedcontinuously to-a reactor, maintained at ademperaturTe of 180?, (3., and a'pifessureiof 200 p.s.-i.g; Airispassed throughthe mixtureiinwthe reactor at theratrof -1'5 ,200. parts .per hour; 25%;rof'; the;oxygefipzissdrthfoughthe reactor is consumed; the balance passing-out withz-the v'entigases. The

water; I V ta'ine tfealfi of Y mxylene containing th balani 'of the reactor is 1 equipped with I a co'ndenser-decanter arrange" ment; .whereby any o-x-ylene and. water in: the vent gases:

condense and separate into two phases, the; o-xyl'ene phase beingxretumedto the: reactor. From the reactor thereiis withdrawxia stream ofthe mixed products-of the reaction; atthe rate"of20,000 parts Eper hour. The contents of the reactor are maintainedate a iconst 'a'nt level and are" agitated thoroughly by the air passing therethrough so that-the stream'ofiproductsis. a: representative sample of the composition of the reactorcontents. This'product stream, containing 12% o-xylene, 55%.. o-tolu'ic acid; 20% phthalide, 6%L-phthalie anhydride; and 7% esters; is fed to :a hydrolyz'enand' extraction col-umn, .both main-tained at a'atemperature at 0., 'lwhere it is combined with 10,000 parts per -hour.-'of-hot water. The resulting'aqueous extract, containing about.2% phthalide and 3% o-toluic acid, besides the phthalic acid',lisl fed continuously to t'he PPr portioni'of a second extraction-column .into which column a stream'of 9700 parts per hour ofo-xylene isfed counter-current to the: aqueous-extract;this-extraction column-beihgaat a temperature: of 100 "C. The' o-xylene' extract from the top of the second column, containing tains aboutl7% 'o-xylene,-55'% o-tol-uic-acid, 20%"phthalide, .1%- phthalic anhydride. and -'7% cof' the esters.

The-aqueous 'rafiinate'trom' therbottoin of -the secondextraction column contains 12% ofifiphthalickacid," and may be fed to any suitable system for the recovery of the phthalic acid as the anhydride.

While water is the preferred solvent for extracting the phthalic acid, as described above, other solvents, such as methanol or ethanol, may be employed for removing this acid from the reaction products, if desired.

It is to be understood that the foregoing detailed description is given merely by way of illustration and that many variations may be made therein without departing from the spirit of our invention.

Having described our invention what we desire to secure by Letters Patent is:

g 1. Process which comprises passing oxygen through a liquid comprising at least 5% by weight of phthalide in the presence of an oxidation catalyst to produce a liquid phase mixture containing phthalic anhydride and removing phthalic anhydride from said mixture.

2. Process which comprises passing oxygen through a liquid comprising at least 5% by weight of each of phthalide, o-toluic acid and o-xylene in the presence of an oxidation catalyst to produce a liquid phase mixture. containing phthalic anhydride and removing phthalic; anhydride from said mixture.

bile from the top of -t his' extractor-there is ob' 3. Process which comprises passing oxygen through a liquid comprising at least by weight of each of phthalide, otoluic acid .and o-xylene, in the presence of an oxidation catalyst. under superatmospheric pressure and elevated temperature to produce a liquid phase mixture containing phthalic anhydride and removing phthalic anhydride from said mixture. 7 g

4. Process which comprises passing oxygen through a liquid comprising at least 5% by weight of each of phthalide, o-toluic acid and o-xylene in the presence of an oxidation catalyst at a pressure between 20 and 1000 p.s.i.g. and a temperature between 100 and 225 C. to produce a liquid phase mixture containing phthalic anhydride and removing phthalic anhydride from said mixture.

5. Process which comprises passing oxygen through a liquid comprising at least 5% by weight of each of phthalide, o-toluic acid and o-xylene at a pressure between 20 and 1000 p.s.i.g. and a temperature between 100 and 225 C. in the presence of an oxidation catalyst comprising a compound of a metal which exists in a plurality of valence states to produce a liquid phase mixture containing phthalic anhydride and removing phthalic anhydride from said mixture.

6. Process as set forth in claim 5 in which said catalyst is a cobalt salt of the group consisting of cobalt acetate and cobalt naphthenate.

7. Process as set forth in claim 2 in which the ratio of o-toluic acid to o-xylene in said liquid is above 3:1.

8. Process as set forth in claim 12 in which the ratio of o-toluic acid to o-xylene in the mixture being oxidized is above 3:1.

9. Process as set forth in claim 12 in which the ratio of o-toluic acid to o-xylene in the mixture being oxidized is about 4 to 6:1.

10. Process as set forth in claim 5, in which the catalyst is a cobalt salt and the water of reaction is removed as it is formed.

11. Process as set forth in claim 10 in which the temperature is 160 to 185 C.

12. Process which comprises oxidizing a liquid phase mixture comprising at least 5% each of o-xylene, o-toluic acid and phthalide in an oxidation zone by passing oxygen therethrough in the presence of an oxidation catalyst to produce a reacted mixture comprising o-xylene, o-toluic acid, phthalide and phthalic anhydride, withdrawing said reacted mixture from said oxidation zone, removing at least a portion of said phthalic anhydride from said withdrawn mixture to produce a remainder con taining a larger proportion of o-toluic acid andphthalide than said withdrawn mixture, and recycling said remainder to said oxidation zone together with a further quantity of o-xylene.

13. Process'whichcomprises oxidizing a liquid phase mixture comprising at least 5% each of phthalide and o-xylene in an oxidation zone by passing oxygen therethrough in the presence of an oxidation catalyst to produce an oxidized mixture comprising o-xylene and phthalic-anhydride dissolved therein, withdrawing said mixture from said reaction zone, hydrolyzing at least a portion of said phthalic anhydride to form phthalic acid and separating said phthalic acid from said oxidized mixture, and'recycling said oxidized mixture, after said separation of phthalic acid, to said oxidation zone together with a further quantity of o-xylene.

14. Process as setforth in claim 13 in which said separation is effected byremoval of an aqueous phase containing said .phthalic acid and immiscible with the said oxidized mixture.

15. Process as set forth in claim 14 and in which the oxidation is in the presence of a catalyst for said oxidation comprising a compound of a'metal which exists in a plurality of valence states and under superatmospheric pressure and at an elevated oxidation temperature.

16. Process as set forth in claim 13 and in which said oxidized mixture contains o-toluic acid. and phthalide, in which said separation is by extraction, and in which, after said extraction, substantially all of said o-toluic acid and phthalide are retained in said oxidized mixture.

17. Process which comprises oxidizing a liquid mixture of o-xylene, o-toluic acid, phthalide and esters produced by said oxidation, at a temperature of about to C., and a pressure of 50 to 200 p.s.i.g., by passing air through said mixture in an oxidation zone in the presence of a cobalt catalyst for said oxidation, said mixture containing about 8 to 13 parts o-xylene, 57 to 61 parts o-toluic acid, 21 to 28 parts phthalide and 5 to 7 parts of said esters together with phthalic anhydride produced in said oxidation, continuously withdrawing a portion of said mixture from said oxidation zone, removing at least part of said phthalic anhydride from said withdrawn mixture, blending said mixture, after said removal of phthalic anhydride, with a further quantity of o-xylene and recycling the resulting blend to said oxidation zone.

References Cited in the file of this patent UNITED STATES PATENTS 2,438,369 Levine Mar. 23, 1948 2,443,832 Morrell June 22, 1948 2,521,466 Levine Sept. 5, 1950 OTHER REFERENCES Elder-field: Heterocyclic Compounds, Vol.2, p. 92- (1951). 

2. PROCESS WHICH COMPRISES PASSING OXYGEN THROUGH A LIQUID COMPRISING AT LEAST 5% BY WEIGHT OF EACH OF PHTHALIDE, O-TOLUIC ACID AND O-XYLENE IN THE PRESENCE OF AN OXIDATION CATALYST TO PRODUCE A LIQUID PHASE MIXTURE CONTAINING PHTALIC ANHYDRIDE AND REMOVING PHTHALIC ANHYDRIDE FROM SAID MIXTURE. 